The configuration of powered underwater vehicles has evolved through many years based on certain understood hydrodynamic and mechanical requirements. Aerodynamic considerations have resulted in somewhat similar shapes for lighter-than-air vehicles such as dirigibles and blimps. Where significant velocity through the fluid medium is required, the art seems to have settled on a generally tubular shape, rounded at the front and tapering toward the rear with the diameter made as small as the internal mechanism and/or flotation requirements will permit to minimize frontal area. This general configuration has been evident in the usual configuration of airships, of manned submarine vehicles, and of unmanned vehicles such as torpedoes. The power required to drive such a vehicle through the fluid medium varies with factors such as the effective frontal area, skin friction, and drag caused by separation of the flow over the surface of the body resulting in turbulence. A conventional way of avoiding flow separation over the rearward surfaces of such vehicles is to provide a tapering surface free of abrupt discontinuities with a propeller or impeller at or toward the rear.
The disadvantages of such structure are that the tapered configuration reduces internal volume while requiring a lengthening of the hull. Further, the control surfaces are located such that actuators therefor, as well as the propeller shaft, must, in part at least, be located where the hull approaches minimum diameter. Thus the traditional shape is volume inefficient, thereby reducing pay load, and makes it inconvenient to adapt the power plant and drive train. Another disavantage of the conventional configuration is that the control fins are normally located in a region where the flow past the fins actually slows in velocity, thus necessitating somewhat larger fins to compensate. And it will be appreciated that the combination of the larger fins and the elongated tapering rear section makes for a somewhat fragile structure, as compared with vehicles having shorter bodies and/or with smaller fins.